Despite intensive investigation, the mechanism of insulin action remains poorly understood. Much evidence suggests that as a consequence of the interaction with its surface receptor insulin initiates a series of reactions which coordinately modify the activity of a number of regulatory enzymes controlling cellular metabolism. It appears that a critical step in this sequence of reactions involves an alteration in protein phosphorylation. In previous studies in adipocytes, we have shown that insulin can alter protein phosphorylation in at least two ways. First, insulin antagonizes cAMP stimulated protein phosphorylation; seccond, insulin promotes a cAMP independent protein phosphorylation. We have hypothesized that insulin achieves this latter effect by the generation of a unique second messenger which alters the activity of certain protein kinases and/or protein phosphatases. In our proposed studies we aim to expand our understanding of insulin's effects on protein phosphorylation with special emphasis on elucidating insulin-sensitive cAMP independent pathways of protein phosphorylation. To achieve this goal, we will address three major questions: (1) What is the mechanism by which insulin rapidly and selectively stimulates the phosphopeptide in adipocytes through a cAMP independent pathway; (2) What is the effect of insulin on overall phosphopeptide metabolism in the isolated rat hepatocyte; (3) By what mechanism does insulin acutely promote the activation of glycogen synthase in the isolated hepatocyte?